There're quite a few ways it could but done, but I'm just gonna assume it'll be a pretty epic scene, if we actually get to see it.
It could be a neat moment: we see YoungKirk admiring the half-built ship, then fade much later when the ship's been completed and is rising into the sky. A formal ceremony introduces the new captain of this ship, and it turns out to be... Christopher Pike. Cue nostalgia moment for 'old-school' fans, while the new viewers are left thinking, "huh? So Kirk isn't the captain? I wonder when and how that's gonna happen..."
:edit: Another thought occurs... Throughout the TV shows and movies, the ships occasionally get very close to stars and even black holes, which have far greater gravity than any planet, especially one as (relatively) small as Earth. If the Enterprise can break away from a black hole, then rising out of a planet's gravity well on its own would be no problem.
Last edited by Big D : 11-16-2008 at 08:28 PM.